17. Presence of any other neurodegenerative disease like parkinson-plus syndromes suspected on neurological examination. These include: multisystem atrophy, progressive supranuclear palsy, dementia with Lewy bodies, and Alzheimer's disease. The presence of some mild parkinsonian features will be accepted since ET is recognized to be associated with overlap symptoms of PD. The mild PD symptoms that will be tolerated for inclusion into the trial include resting tremor, bradykinesia, and rigidity.